1. Field of the Invention
The present invention relates to a disk apparatus, in particular, to an optical-disc data reproducing apparatus having an advance reading function, and using a CLV (Constant Linear Velocity in disc rotation) method.
2. Description of the Related Art
A CD (Compact Disc) has been widely used for reproducing music tunes. However, use of the CD as a data recording medium especially for only reading data therefrom is beginning to increase, a CD so used being referred to as a CD-ROM. There are various types of drive apparatus for CD-ROMs (referred to as CD-ROM apparatus, hereinafter) having a function of double and/or triple disc-rotation-speed driving.
The double or triple disc-rotation-speed driving is such that the disc is rotated in such a CD-ROM apparatus at a rotation speed double or triple a disc rotation speed (1.2 through 1.4 m/s) at which a disc is rotated in a CD player for reproducing music tunes. Generally speaking, by increasing a disc rotation speed, it is possible to increase a data transfer rate.
Along with the increased data transfer rate, an advance reading function is being used. The advance reading function will now be described. A buffer memory is provided in a CD-ROM apparatus. When a host computer requests the CD-ROM apparatus to read out a certain block of data from a disc used as a data recording medium, the CD-ROM apparatus reads not only the thus-requested block of data but also a number of block of data from the disc. The thus-read number of blocks of data are those located immediately preceding or immediately subsequent to a location of the requested block along tracks of the disc. The thus-read number of blocks of data is stored in the buffer memory. Then, when the host computer subsequently requests the CD-ROM apparatus to read a certain block of data, the CD-ROM apparatus searches the number of blocks of data thus stored in the buffer memory. When the currently requested block of data is advantageously included in the stored number of block of data, the relevant block of data is transferred to the host computer from the buffer memory. Such an advantageous case is referred to as a cache-hit case or cache-hitting.
When the host computer requests the CD-ROM apparatus to transfer a certain block of data, the CD-ROM apparatus performs a seeking operation so as to search the disc for the requested block of data, reads it and transfers it to the host computer. Subsequently, the CD-ROM apparatus continues to read a number of blocks of data which are located immediately preceding or immediately subsequent to a location of the currently requested block of data along tracks of the disc. The thus-read number of blocks of data are stored in the buffer memory. An operation of reading the number of blocks of data and storing them in the buffer memory is referred to as an advance reading operation.
When the host computer requests the CD-ROM apparatus to transfer a certain block of data while performing the advance reading operation and the thus-requested block of data is not present in the buffer memory, the CD-ROM apparatus either continues the currently performed advance reading operation until the requested block data is thus reached or terminates the advance reading operation and performs a seeking operation to search the disc for the currently requested block of data. Thus, the CD-ROM apparatus obtains the requested block of data from the disc and transfers it to the host computer.
Whether the currently performed advance reading operation is continued until the requested block data is reached or the advance reading operation is terminated and a seeking operation is performed to search the disc for the requested block of data is determined using a predetermined reference number of blocks. Specifically, if a number of blocks of data present between a currently read block of data in a currently performed advance reading operation and a currently requested block of data is equal to or less than the predetermined reference number, the currently performed advance reading operation is continued. If the number of blocks of data present between the currently read block of data in the currently performed advance reading operation and the currently requested block of data is more than the predetermined reference number, the advance reading operation is terminated and a seeking operation is performed. Thus, it is possible to effectively reduce a time required for reaching, reading and transferring a requested block of data.
Such a CD-ROM apparatus uses the above-mentioned CLV method and thus a number of blocks of data stored in a single track of inner tracks is different from a number of blocks of data stored in a single track of outer tracks of a disc. Specifically, the number of blocks of data stored in a single track of outer tracks is as large as more than twice the number of blocks of data stored in a single track of inner tracks of the disc. Accordingly, during the seeking operation in which a read/write pickup of the CD-ROM apparatus jumps to a target track of the disc, a maximum time required for waiting for a target block of data is different between the inner tracks and outer tracks.
(In a case where the disc has a track format such that the tracks form a spiral, only one spiral-shaped track is formed on the disc. However, for the sake of simplification of description, when the pickup moves substantially perpendicular to a track extending line and thus reaches a track portion located laterally in parallel to a track portion at which the pickup has been located, it is expressed that `the pickup jumps to a different track`, in the specification and claims. Further, in this case, a turn among turns of the spiral track will be referred to as `a track`.)
In fact, in a case where the target block of data passed through immediately before the pickup has reached the target track as a result of jumping, it is necessary for the pickup to wait for the target block of data to reach the pickup and thus wait for an approximately full turn of the disc. In other words, in this case, it is necessary for the pickup to wait for the target block of data to reach the pickup and thus wait for approximately a whole number of blocks of data present in the track to pass through. A time required for the target block of data to reach the pickup in such a case is the maximum time.
Therefore, because a number of blocks of data present in a single track of the outer tracks is larger than that of the inner tracks, the maximum time required for a target block of data reaching the pickup after the pickup has reached a relevant track in a case where the target block is present in the track of the outer tracks is longer than that in a case where a target block is present in a track of the inner tracks.
In description concerning the present invention, an expression such as `the pickup reaches a target block of data` is used in such a case as that in which the pickup reaches a target track as a result of the seeking operation of the pickup and then a target block of data stored in the target track reaches the pickup as a result of a rotation of the disc.
In the CD-ROM apparatus in the related art, the above-mentioned predetermined reference number of blocks to be used for determining, in response to a transfer request during an advance reading operation, whether the advance reading operation is continued or a seeking operation is proceeded with is a single fixed number for the inner and outer tracks of the disc. Accordingly, if, for example, the predetermined reference number of blocks is determined according to a number of blocks of data present in a track of the inner tracks, although a target block of data is present in a track of the inner tracks, it is possible to effectively reduce a time required for the pickup to reach the target block of data as a result of determining an operation, to be performed, using the predetermined reference number of blocks.
However, if a target block of data is present in a track of the outer tracks, when the same predetermined reference number of blocks is used for determining an operation to be performed and as a result it is determined that a seeking operation is performed, it may not be possible to effectively reduce a time required for the pickup to reach the target block of data. Specifically, although this predetermined reference number of blocks of data is used and thus it is determined to perform a seeking operation, a time required for the pickup to reach the target block of data if a currently performed advance reading operation were continued may have been shorter than that in the case of performing the seeking operation. Thus, it may not be possible to effectively reduce a time required for the pickup to reach a target block of data and thus a data transfer rate may be degraded.